7.3.101
अतो दीर्घो यञि
Operational rule vidhi
The last letter of an अदन्त अङ्ग becomes दीर्घ when followed by a यञादि सार्वधातुक प्रत्यय.
Word by word (padaccheda)
Target अतः ṣaṣṭhī · ekavacanaSubstitute / term prathamā · ekavacanaRight context saptamī · ekavacana
- Target Ṣaṣṭhī (6th case): names what gets replaced, "in place of X" (1.1.49 षष्ठी स्थानेयोगा).
- Substitute / term Prathamā (1st case): in operational rules, the substitute or the thing introduced; in definitions, the term or its referent.
- Right context Saptamī (7th case): "when X follows", the operation applies to what precedes (1.1.66 तस्मिन्निति निर्दिष्टे पूर्वस्य). Also a condition or domain ("in the sense of").
Dotted words are technical terms, dashed ones pratyāhāras (names for classes of sounds or affixes). Hover or tap one to see its card.
Full reading
अतः
Pāṇini leaves out words that carry over from earlier sūtras. Expand to see the rule as a reader actually understands it.
अतः → /
Replace ataḥ with dīrghaḥ when yañi follows. Inherited words (anuvṛtti) may add further conditions.
Commentary
The long आ is substituted for the final अ of a tense अङ्ग (stem) before a सार्वधातुक affix beginning with a व् or म् (literally a consonant of यञ् प्रत्यहार).
As पचामि, पचावः, पचामः, पक्ष्यामि, पक्ष्यावः, पक्ष्यामः ॥ Why 'for the अ only'? Observe चिनुवः, चिनुमः ॥ Why before a यञ् consonant (semivowels, nasals and झ and भ) only? Observe पचतः, पचथः ॥ Why a 'Sarvadhatuka'? Observe अङ्गना, केशवः ॥ Some read the anuvritti of तिङ् into this sutra, from 7.3.88 so that the lengthening takes place only before Personal-endings. According to them before क्वसु there is no lengthening, as भववान् ॥
The word भववान् is thus formed. To भू is added क्वसु, then comes शप्, treating kvasu as a sarvadhatuka under 3.4.117; the reduplication of the root ending in शप् is prevented, because the word dhatu is used in 6.1.8 which ordains reduplication of a root only, and not of a root plus a vikarana like the form भव (भू + शप्) ॥ Those who do not read the anuvritti of तिङ् in this sutra, but only of the word सार्वधातुके, they explain the form भववान् as a Vedic anomaly.
Śrīśa Chandra Vasu, The Ashtadhyayi of Panini (1897), via ashtadhyayi.com.